Diesel’s competitors

| April 02, 2008

Caterpillar does not recommend biodiesel in 2007 engines because of the U.S. Environmental Protection Agency’s mandated maintenance intervals for the diesel particulate filter, Powers says. The Caterpillar Regeneration System has a small injection nozzle that needs periodic cleaning with a fuel additive, a procedure done at the same time as DPF ash cleaning. Biodiesel can cause the nozzle to clog too early, Powers says.

Caterpillar and all the engine companies generally support biodiesel in earlier engines, however, because it reduces trucks’ carbon footprint by effectively recycling carbon dioxide, Powers says.

“Our biggest concern is that there is not enough consistency across the country,” he says. “At present, the states don’t have the regulators in place, the weights and measures people who verify that normal diesel fuel meets the ASTM D975 specification.”

The Engine Manufacturers Association is working on a “more robust” and complete specification than the present one, Powers says. In the meantime, biodiesel may not be worth the risk “unless you know your supplier can deliver the specification consistently,” he says.

The National Biodiesel Board is attempting to get as many refiners as possible to achieve BQ-9000 certification, which guarantees consistent refining to the ASTM standard and verification through constant testing.

Natural gas
A surprising alternate fuel for diesels is natural gas, made up mainly of methane. Whereas diesel is about one-third carbon – meaning that diesel engines, even when yielding perfect combustion, produce a substantial amount of CO2 – methane is only one-fifth carbon. Its simple, gaseous structure makes it burn relatively cleanly and with almost no soot. Its high hydrogen-to-carbon ratio means inherently lower greenhouse-gas emissions.

Powers says Caterpillar does not see natural gas as a viable truck fuel. The ideal natural-gas application is a fleet with vehicles that return regularly to a home base within reach of city gas mains.

However, Cummins-Westport, a joint venture of Cummins and Westport Power Inc., has been producing liquid natural gas ISX engines for years, and the ports of Los Angeles and Long Beach plan to spend $1.6 billion on Kenworth T800s equipped with these engines as part of its Clean Truck’s Program. Pacific Gas and Electric in San Francisco also has purchased some of these vehicles and is the nation’s first utility to operate Kenworth T800 LNG-powered vehicles.

These are basic Cummins designs with altered fuel injection. Medium-duty Cummins natural gas engines include a spark ignition system and a different combustion chamber.

Because natural gas cannot be liquefied by pressure alone, such trucks require heavily insulated tanks – designed like thermos bottles – that keep the gas liquiefied at about minus 250 degrees Fahrenheit. LNG supplier Clean Energy runs fueling stations around major cities in various areas, including Southern California and Texas. Fueling is fast. Both saddle tanks can be filled with a single connection on one side of the truck.

The well-insulated tanks retain the fuel without a significant pressure increase, although if the truck sits for seven to 10 days in warm weather, the tank may vent a small amount of gas.

Testing has confirmed the integrity of the tank even when dropped eight stories. How about a severe, T-bone crash that could rupture a tank? Because the gas is lighter than air, it would rapidly escape skyward, making an explosion unlikely, says Jonathan Burke, a Westport Power vice president.

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